cars and Japanese density, updated model

[mindstalk]

Something I've been struggling with recently: my various models of a city built around cars yield numbers similar to actual densities. My models of human oriented cities yield much higher densities than the real cities that inspire them. But I think I've realized at least part of why.

To recap:

Car city model: assume 1/3 is streets/roads, 1/3 is zoned residential, 1/3 commercial. Assume half the commercial land is surface parking, at 30 m2/space. A model km2 thus can have 1e6 m2/6/30 m2/space = 5555 parking spaces; at 3 non-residential spaces per car, that's 1851 cars. Multiply by 1.25 for non-drivers, and get a population density of 2300 people/km2, which is about as dense as post-war cities get in the US.

People city model: 1/3 street, and the rest with an average residential FAR of 2.0, whether that's residential neighborhoods with houses or mixed/commercial neighbhoods with housing above shops. That's 1.3e6 m2 of living space per km2, allowing 33,000 people at 40 m2 per person (reasonable to me) or 16,600 people at 80 m2 per person (current US average).

Osaka and Tokyo, which at least *look* like they should be hitting FAR 2 or greater -- lots of 2 story houses filling their lots, lots of high rises -- are 12,000 and 15,000 people/km2, at only 19 m2 per person. That's off by a factor of 4.

But my people model assumes no cars at all, or that they can treated as trivial. In fact Japan supposedly has a lot of cars, 0.6 per person nationwide. Assuming only 2 parking spaces per car, that's 0.6*2*30 = 36 m2 of parking per person, while nationwide there are 22 m2 of living space per person. So there's as much, or more, parking than living space, even in Japan. The cities would have fewer cars but also less space per person.

And that's cars parked in multi-level garages taking half of the built up floor area. Much of the urban parking is actually open surface lots, whether small commercial lots in neighborhoods or parking attached to stores. When all the surrounding building is lot-filling 2+ story buildings, each 30 m2 of surface parking displaces 60 or more m2 of floor space.

So there's a factor of 2. It's also possible I overestimate the average residential FAR, not accounting for industrial zones or parks and shrines or overestimating mixed buildings, I dunno.

This adjusted model implies that a huge chunk of Tokyo buildings are parking, which wasn't my impression, but also wasn't something I was paying attention to. Of course, I was also mostly in places not far from train lines.

Hmm, this says that in new Tokyo (23 wards) condominiums, the ratio of parking to spaces is 30% -- 2064 spaces for 7008 apartments. But in 2007 the ratio was 56%. I don't know how big these condos are: studios, 2BR, what? Or how many people are in each one. But an average of 15 m2 of parking attached to each not very big condo is a fairly sized chunk.

Caveat: Japanese cars are smaller; there's also robotic parking that I assume takes less space overall. Houses can have parking lots that go directly to the street and thus don't need access lanes, though these are often open surface parking that displace multi-story density above them.

This is tangentially fascinating -- cities limited wheeled carts even before cars, with most transport by canal; most canals were later filled in to make arterial roads; less than 2% of Japanese streets are wider than 5.5 m, and 35% are too narrow for even one car.

I have failed to find how many parking spaces Japan or its cities have.

Comments

[mtbc]

The fancy condos in Manila I stayed in had maybe thirty-ish floors of apartments then a couple of floors of car-parking underground. I wasn't much paying attention though.